Recent studies using a combination of antiretroviral drugs have shown a dramatic decrease in levels of plasma virus in HIV-infected individuals. The rapid decline shows that virus production results largely from continuous rounds of virus infection of and replication in host cells with rapid turnover of both free virus and virus-producing cells. Following the rapid decline, plasma virus decays at a much slower rate reflecting the turnover of chronically or latently infected cells. It has been shown that latently infected resting CD4+ T cells with the integrated form of HIV DNA exist in vivo in HIV-infected individuals and that these cells can give rise to infectious virus upon cellular activation. However, it is not clear whether such cells persist in the face of a potent combination therapy consisting of 3 antiretroviral drugs. Knowing the size and the half life of the latent virus reservoirs in individuals treated with the 3-drug regimen is therefore extremely important not only to evaluate and design anti-retroviral drugs but also to better understand the pathogenesis of HIV-1 infection. In this project, we are investigating whether a long-term virus reservoir, such as resting CD4+ T cells with integrated HIV-1 provirus, is present in HIV-infected individuals treated with 3 antiretroviral agents that have suppressed plasma viremia to undetectable levels. In addition, upon recovery in vitro of infectious virus from latently-infected resting CD4+ T cells, the phenotype of the virus will be determined.